The present invention relates to improved oil based compositions for temporarily sealing subterranean zones and methods of utilizing the compositions.
In the drilling of oil and gas wells using the rotary drilling method, drilling fluid is circulated through the drill string and drill bit and then back to the surface by way of the well bore being drilled. The drilling fluid maintains hydrostatic pressure on the subterranean zones through which the well bore is drilled and circulates cuttings out of the well bore. During such drilling, subterranean vugs, fractures, and other thief zones are often encountered whereby the drilling fluid circulation is lost, and drilling operations must be terminated while remedial steps are taken. Also, when a subterranean zone is penetrated containing fluids under pressure which exceeds the hydrostatic pressure exerted on the zone by the drilling fluid, formation fluid crossbows and/or underground blow-outs can and often do occur. As a result, drilling fluid circulation is often lost which requires the termination of the drilling and the implementation of remedial procedures which are often of long duration and high cost.
U.S. Pat. No. 6,060,343 issued May 9, 2000 having inventors Ronald E. Sweatman and James F. Heathman and issued to Halliburton Energy Services, Inc. describes oil based compositions and methods of using the compositions for sealing subterranean zones. The compositions are basically comprised of oil, a hydratable polymer, an organophilic clay, and a water-swellable clay. These compositions and methods develop ultra high viscosity in a few seconds or minutes, solving many problems associated with prior art methods and compositions, and have been highly successful for sealing subterranean zones. The specification of U.S. Pat. No. 6,060,343 is incorporated herein by reference in its entirety.
It is sometimes desirable, however, to temporarily seal a subterranean zone. Thus, there is a need for improved compositions and methods for sealing subterranean zones having the benefits and advantages of the compositions disclosed in U.S. Pat. No. 6,060,343 and that would have the additional benefit of temporarily sealing subterranean zones. After having been sealed for the desired well workover activity, it would be desirable to be able to easily and quickly reopen the subterranean zones. It would still be important, however, that such a seal not be easily washed out or removed until it is desired to remove the plug and reopen the zone.
Improved oil based compositions for temporarily sealing subterranean zones and methods of using the compositions are provided and meet the need described above. The compositions are basically comprised of oil, a hydratable polymer, an organophilic clay, a water-swellable clay, and an acid soluble material. These compositions will form a viscous gel when contacted with water. The gelled mass may then be dissolved with an acidic fluid, such as 15% hydrochloric acid in water. Thus, the temporary seal is not easily washed out or removed until it is desired to remove the plug and reopen the zone The compositions can also include cross-linking agents, dispersing agents, cement, fillers and the like, provided that any such other materials do not adversely affect the desired functions of the compositions according to the invention.
When the temporary sealing compositions of this invention contact water in the well bore, the hydratable polymer reacts with the water, whereby it is hydrated and forms a highly-viscous gel and the water-swellable clay swells, whereby an ultra high viscosity mass is formed. The organophillic clay adds viscosity to the sealing composition when it is formed, i.e., it reacts with the oil carrier fluid and prevents the polymer and water-swellable clay from settling out of the composition.
When the temporary sealing compositions of this invention contact water in the well bore, the hydratable polymer reacts with the water, whereby it is hydrated and forms a highly-viscous gel and the water-swellable clay swells, whereby an ultra high viscosity mass is fanned. The organophilic clay adds viscosity to the sealing composition when it is formed, i.e., it reacts with the oil carrier fluid and prevents the polymer and water-swellable clay from settling out of the composition.
A composition for temporarily sealing a subterranean zone to prevent the uncontrolled flow of fluids into or from the zone preferably comprises: first component comprising oil; the balance of the temporary sealing composition comprising a second component and a third component, wherein the second component comprises: a hydratable polymer, an organophilic clay, and a water-swellable clay; and the third component comprises an inorganic material that is readily acid soluble but substantially insoluble in neutral or basic water; wherein the second component is present in an amount in the range of from about 10% to about 90% by weight of the balance of the temporary sealing composition, and wherein the third component is present in an amount in the range of from about 10% to about 90% by weight of the balance of the temporary sealing composition.
Preferably, the second component comprises: a hydratable polymer present in an amount in the range of from about 4.4% to about 14.6% by weight of the second component; an organophilic clay present in an amount in the range of from about 0.4% to about 1.6% by weight of the second component; and a water-swellable clay present in an amount in the range of from about 84% to about 95% by weight of the second component.
The methods of the invention comprise the steps of preparing a temporary sealing composition of this invention, introducing it into the subterranean zone to be sealed, and subsequently removing the temporary sealing composition by washing with an acidic solution.
It is, therefore, a general object of the present invention to provide improved oil based compositions and methods for temporarily sealing subterranean zones and methods. Other and further objects, features, and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.